Technology that understands the set of people that with whom a user interacts over time has applications in context aware computing systems. For example, such technology can help a user understand and review how much time he/she spent with different people over time and as a consequence help the person in improving his/her social life. Alternatively, it can help identify a set of people who are currently involved in an activity together which provides group context for the context aware system. For example, ambient displays or kiosks can automatically adapt to the group context instead of relying on individuals' context. Thus, systems and methods for proximity detection may find utility.